Engine: Description and Operation
Operation
The V8 engine is an eight cylinder, water cooled unit comprising of cast aluminium cylinder block and cylinder heads.
The two banks of cast iron cylinder liners are shrink fitted and are located on stops in the cylinder block. The banks of cylinders are set at 90 ° to each other. The crankshaft is carried in five main bearings, end-float being controlled by the thrust faces of the upper centre main bearing shell.
Engine without suffix B added to serial no. illustrated
The centrally located camshaft is driven by the crankshaft via an inverted tooth chain. The valves are operated by rockers, pushrods and hydraulic tappets. The distributor - if fitted, is driven by a skew gear from the front of the camshaft.
The aluminium alloy, pistons have two compression rings and an oil control ring and are secured to the connecting rods by semi-floating gudgeon pins. On later 4.2L engines the gudgeon pin is offset 0.5 mm (0.02 in), identified by an arrow mark on the piston crown, which must always point to the front of the engine. Plain, big-end bearing shells are fitted to each connecting rod.
Lubrication - Engine numbers without suffix B
Lubrication - Engine numbers with suffix B
Engine numbers without suffix B
The full flow lubrication system uses an external gear pump which is driven by the distributor drive shaft. The oil pump gears are housed in the timing cover and the oil pressure relief valve and warning light switch are fitted to the oil pump cover.
Engine numbers with suffix B
The full flow lubrication system uses a gear type oil pump driven from the crankshaft. The assembly is integral with the timing cover which also carries the full flow oil filter, oil pressure switch and pressure relief valve.
All engines
Oil is drawn from the pressed steel sump through a strainer and into the oil pump, excess pressure being relieved by the pressure relief valve. The oil pressure warning light switch is screwed into the oil pump cover and registers the oil pressure in the main oil gallery on the outflow side of the filter. Pressurized oil passes through an oil cooler - if fitted to the full flow oil filter and through internal drillings to the crankshaft where it is directed to each main bearing and to the big end bearings via Nos. 1, 3 and 5 main bearings. An internal drilling in the cylinder block directs oil to the camshaft where it passes through further internal drillings to the hydraulic tappets, camshaft journals and rocker shaft. Lubrication to the thrust side of the cylinders is by oil grooves machined in each connecting rod big end joint face, which are timed to align with holes in the big end journals on the power and exhaust strokes.
Distributor drive and timing chain lubrication
The distributor drive and timing chain are lubricated from the camshaft front bearing. The feed to the timing chain is channelled along the camshaft sprocket, key and spacer.
Hydraulic tappets
The purpose of the hydraulic tappet is to provide maintenance free and quiet operation of the inlet and exhaust valves. It achieves this by utilizing engine oil pressure to eliminate the mechanical clearance between the rockers and the valve stems.
During normal operation, engine oil pressure present in the upper chamber passes through the non-return ball valve and into the lower, high pressure, chamber.
When the cam begins to lift the outer sleeve, the resistance of the valve spring felt through the push rod and seat causes the tappet inner sleeve to move downwards inside the outer sleeve. This downward movement of the inner sleeve closes the ball valve and increases the pressure in the lower, high pressure chamber, sufficiently to ensure that the push rod opens the valve fully.
As the tappet moves off the peak of the cam the ball valve opens to equalize the pressure in both chambers which ensures the valve closes when the tappet is on the back of the cam.